1. Field of the Invention
An aspect of the present invention relates to a spring assembly to be used as, for example, a return spring for a multi-plate clutch piston in a clutch mechanism of an automatic transmission of an automobile.
2. Description of the Related Art
JP-2005-024003-A discloses a spring assembly including two annular plates and plural coil springs interposed between the two annular plates. In the spring assembly, an end turn portion (end portion) of the coil spring is inserted into a cylindrical projecting portion extending from each annular plate, and then a distal opening edge of the cylindrical projecting portion is flared to stake (fix) the end turn portion of the coil spring to the cylindrical projecting portion of the annular plate.
In the spring assembly, when a large axial tensile force acts on the coil spring, the end turn portion of the coil spring may be expanded to climb over the distal opening edge of the cylindrical projecting portion, and the coil spring may come off the annular plate.
In a spring assembly disclosed in JP-UM-S61-112139-A, a coil spring has an end turn portion broadened in a radial direction as compared with a second-stage (or higher-stage) turn. For example, the end turn portion of the coil spring is inserted into a cylindrical boss extended from a substrate, and a stepped cover is attached onto the substrate, thereby sandwiching the end turn portion of the coil spring broadened in the radial direction by the stepped cover and the substrate in an axial direction.
In the spring assembly of JP-UM-S61-112139-A, the end turn portion of the coil spring may not come off the substrate. However, since the end turn portion of the coil spring is broadened in the radial direction and the stepped cover is provided in addition to the substrate and coil spring, the manufacturing process is cumbersome and complicated.